In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be glamorized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, while a polishing liquid containing abrasive particles such as silica (SiO2) or cerin (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing surface and polished using the polishing apparatus.
A polishing apparatus for performing the above CMP process includes a polishing table having a polishing pad, and a polishing head for holding a substrate such as a semiconductor wafer. When the substrate is polished by using such a polishing apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the polishing head. At this time, while a polishing liquid (slurry) is supplied onto the polishing pad, the polishing table and the polishing head are moved relative to each other to bring the substrate into sliding contact with the polishing pad, so that the surface of the substrate is polished to a flat mirror finish.
In the polishing process, the component concentration or the like of the polishing liquid affects the polishing performance. Japanese Laid-open Patent publication No. 2011-167769 discloses a polishing method in which a polishing liquid discharged from a polishing apparatus is recovered in a recovery container, and the zeta potential of the recovered polishing liquid is measured, and if the measured zeta potential is lower than a predetermined value, a zeta potential adjuster is added to the recovered polishing liquid to disperse agglomerated polishing abrasive particles, and then the polishing liquid whose zeta potential is not less than a predetermined value is circulated back into the polishing apparatus.
Further, Japanese Laid-open Patent publication No. 2007-520083 discloses a CMP apparatus in which a waste liquid (containing debris, polishing slurry, and chemical by-products or other by-products) discharged from a polishing pad in an adjustment process for controlling various steps of a planarizing process is recovered in an analyzing unit, and a factor such as a predetermined element concentration in the recovered waste liquid is analyzed to evaluate the property of the waste liquid, and then the planarizing process is controlled based on the evaluated property of the waste liquid.
In a polishing apparatus for performing the CMP process, during the CMP process, a polishing liquid is supplied onto a polishing pad at all times, and is then discharged as a waste liquid from the polishing pad at all times. The polishing liquid that has been supplied onto the polishing pad includes a large quantity of polishing liquid that has hardly contributed to the polishing process and has discharged from the polishing pad while leaving its polishing capability. Therefore, the polishing capability of the polishing liquid supplied onto the polishing pad is not utilized to the maximum, and the polishing liquid which retains a sufficient level of polishing capability is discharged.
Heretofore, as disclosed in Japanese Laid-open Patent publication Nos. 2011-167769 and 2007-520083, it has been the customary practice to recover the polishing liquid (or waste liquid) discharged from the polishing apparatus, and to measure and analyze the component concentration or the like of the recovered polishing liquid (or waste liquid). In this case, the recovered polishing liquid (or waste liquid) contains debris (polishing debris), polishing slurry, and chemical by-products or other by-products. Therefore, even if the polishing liquid discharged from the polishing apparatus is recovered and the recovered polishing liquid (or waste liquid) is measured and analyzed, this does not mean that the polishing capability that has been held by the polishing liquid at the time of actual polishing or immediately after actual polishing is measured.